This project is for the purpose of gaining information concerning the nature and mechanism of production of abnormalities of the serum complement system in glomerulonephritis. The C3 nephritic factor, found in patients with membranoproliferative glomerulonephritis, is being isolated, antibody made to it, and its reaction mechanism studied. Techniques being used for the isolation include precipitation with polyethylene glycol, with caproic acid, and column chromotography. Studies are being done on the in vivo immune reaction occurring in patients with the nephritis of chronic bacteremia to determine its relation to the glomerulitis. The complement profile, composition of the cryoprecipitate, the bacterial antigens and antibodies present in serum and plasma are being measured and characterized. Finally, the interrelationships in the serum concentrations of the C3b inactivator and the C3 proactivator proteins in normal persons and in patients with various nephritides and sickle cell disease are being characterized. It appears that the serum concentration of these two proteins are directly related in normal subjects and those with membranoproliferative glomerulonephritis but in lupus nephritis and sickle cell anemia the relationship deviates from normal.